It is slightly unfair to complain about what platforms a developer chooses to publish his/her work on. Perhaps they have been a long term Apple user? Perhaps they don't know anything about Windows development.
Windows may be the largest, but there are so many good apps and developers making a living off the smaller platforms. This doesn't make using their apps a "non-starter".
I don't think the parent meant a "non-starter" in general. This app seems really awesome, but I primarily develop on Windows, so it's a non-starter for me, which is really too bad. I was really excited looking through the page until I noticed it was only on OS X.
That and I'd prefer my electronic notebook to be available on my phone as well, so that's another reason I wouldn't use it. But if this ever comes out for Windows/Android, I'd definitely be excited to try it out.
There are so many platforms available. I don't think apps would ever get released (or companies started) if for people to adopt them they had to be out for every desktop and mobile platform. That is unreasonable. Get something out there and iterate on it.
I prefer not to use my phone and tablet for stuff like this. It forces me to pay attention to it more than I wold like because I am carrying the device. I force myself to take breaks from work by not having work stuff on my phone. If one of my co-workers really wants me, they have my phone number.